The selection and training of oarsmen in the sport of competitive rowing would be greatly facilitated by on-water measurements providing quantitative data from which the individual as well as the collective performance of the crew members can be determined. A fundamental quantity for the assessment of performance is the effective force which an oarsman exerts on the oar handle or, alternatively, the reactive force produced by the oarsman's feet pushing on the stretcher of the rowing shell, exercise machine or other rowing apparatus. It would therefore be desirable to provide a device which produces a signal that is proportional to this effective force. By definition, the "effective force" is the longitudinal (axial) component of the applied force. It is this component which is responsible for the propulsion of the rowing shell. Therefore, it would further be desirable to provide apparatus that measures effective force while the shell is in use, i.e., "on-water" in addition to being useful in rowing simulators or other equipment.
The on-water measurements of rowing performance reported to date have primarily been the result of research programs relating to the biomechanical aspects of rowing. The apparatus involved in these studies has been generally quite complex and sophisticated. These investigations cover a wide range of variables and are geared to measuring a multitude of forces such as the forces acting on the oar, the oar locks, and, to a lesser extent, on the foot stretcher. These data are generally reported relative to a time base or as averages taken over specific time intervals. For example, force measurements obtained from the oar locks are frequently used to calculate the work done and/or the power developed by an oarsman. However, no practical device has been developed that can be used onwater for crew selection and for routine training purposes using either on-water tests or using rowing simulators.
A system designed by the inventor of the present invention and used by the University of Pennsylvania varsity crew team from 1964 to 1966 made use of an oarlock that was specially constructed to be restricted to move only in the longitudinal direction by a mechanical slide. Displacement of the oarlock and slide assembly compressed a spring and caused the sequential closing of four switches at predetermined force levels. Each oarsman was provided with a set of four lights; the first light was activated at a threshold force of 200 pounds of force and the other three lights were activated sequentially in increments of 25 pounds. A panel containing the composite readout for all eight oarsman could be viewed by the coxswain or from the coach's launch. The use of this system was discontinued due to the extensive maintenance required for the electromechanical components.
The apparatus discussed immediately above provided measurements of the force acting on the oarlock, and though it can be used for research purposes, it has many practical disadvantages. First, the oarlock must be modified in order to incorporate a linear sensing element. Further, some mechanical or electrical apparatus must be added to the oarlock in order to measure the longitudinal component of the applied force. The most serious drawback, however, is the difficulty in transferring the modified oarlock arrangement from one shell to another, as would be necessary, for example, if both heavyweight and lightweight crews were to be evaluated. Another major problem, as explained above, is the vulnerability of the modified lock and the associated wiring to mechanical damage. Finally, if the shell is rigged for sculling, both oarlocks should be instrumented, adding to the cost and complexity of the system.
Others have attempted to measure force using the oar itself as an elastic member to make force measurements. From a practical viewpoint, however, there are many serious objections to this scheme, quite aside from the difficulty of affixing a strain sensing element to the oar. First, the determination of the effective force exerted by the oarsman requires continuous measurement of the angular displacement of the oar. Therefore, some type of displacement resolution must be incorporated into this type of force measurement system. Secondly, both the sensing element and the wiring connecting it to the shell are extremely vulnerable, especially since the electrical connections to the oars must be disconnected when the boat is stored after a workout. Also, there is the problem of calibration since the elastic properties of the materials used in shells and oars are often sensitive to temperature. Finally, for sculling, both oars should be instrumented if the information relating to the performance is to be complete.
Thus, there remains an unmet need for apparatus capable of accurately measuring the force applied to an oar. In order to overcome the shortcomings of the prior art, such a system should be rugged and reliable, while altering the standard shell arrangement as little as possible.